Pipelines used for transmission of fluids under pressure, such as natural gas, include pipeline valves, used for a variety of purposes. The pipeline valves may be designed to automatically close under certain conditions, such as when there is a substantial drop in pipeline pressure, due to a line break or the like. Actuating systems for pipeline valves have therefore been developed which operate from an auxiliary source of pressure fluid supplied from the pipeline in which the valve is installed. Such systems are referred to as “air over oil” actuators, wherein a hydraulic fluid is subjected to pressure from the pressurized fluid from the pipeline or other auxiliary pressure source to cause actuation of the valve. One such actuation system is described in U.S. Pat. No. 2,738,945, which shows use of such a system in conjunction with a vane type pipeline valve. Other types of pipeline valves include rack in pinion rotary valves or other suitable rotary valve configurations. In the prior actuation systems, although the “air over oil” system to operate the valve provides smooth and effective valve actuation, there are problems associated with such systems which cause significant problems for the pipeline operator. In known systems, hydraulic fluid reservoirs are oriented vertically and pressure from the pipeline is supplied to the reservoir from the top side thereof via a poppet block or control valve. In many cases, the control valve can fail, allowing pressurized fluid from the pipeline to blow through the control valve. The control valve exhausts to the atmosphere upon failure, and this action causes a siphoning effect within the reservoir, resulting in draining the hydraulic fluid from the system and to the exterior of the system or into external environment. As should be recognized, if hydraulic oil is exhausted to the external environment in this fashion, it causes a significant environmental concern. In such cases, pipeline operators are typically required to expend significant sums to clean up any exhausted hydraulic oil, which is exacerbated by the remote location of such valves.
It would therefore be beneficial to provide a pipeline valve actuating system which avoids these problems of the prior art, and provides for smooth and effective operation of the valve in an automatic fashion.
Another deficiency with respect to the prior art actuating systems is found in that once the control valve fails and hydraulic oil is exhausted from the system, it is then not possible to override the automatic actuating system by means of a manual safety override. With hydraulic oil exhausted from the system, the safety override provided in prior systems is rendered ineffective. Such safety overrides are required in the event that pipeline pressure has completely failed. It would therefore be advantageous to prevent exhaustion of hydraulic fluid from an actuating system, to ensure that manual safety overrides remain operational.